IntelliJ IDEA 2016.3 Help

Analyzing Data Flow

Introduction

IntelliJ IDEA provides Dataflow Analysis features to help you with code archeology - better understand the
inherited project code, interpret complicated parts of the code, find bottlenecks in the source, and more.

Specifically, Dataflow to/from here features allow you to:

See where values assigned to a variable come from.

Find out all the possible values that a variable can have.

Find out the places an expression\variable\method parameter can flow into.

Reveal the places where potential NullPointerException can arise.

If you want to trace back the value passed to a parameter at caret, you can create a
slice view of the source code using the
Analyze | Dataflow to Here command. Moreover, using
Analyze | Dataflow from Here
command you can find the places an expression can flow into.
The results of each dataflow analysis are displayed in the dedicated tabs of the
Analyze Dataflow tool window.

Examining the results of Dataflow analysis

The following sections briefly describe how to "read" the dataflow analysis results.

Dataflow to Here

Expand the tree to dig in the chain of assignments and method calls that lead to the symbol in question.
Nodes with gray background denote duplicates (the usages that are already present in the tree in another location).
The image below shows an example of the Dataflow to Here analysis results:
The values in this view flow in the following direction:
the value for the field String authType in SingleSignonMessage
comes from the this.authType = authType assignment statement in
SingleSignOnMessage.setAuthType() method called from
ClusterSingleSignOn.register() method with authType
parameter and so on.

To find out what are the possible values a symbol can have, click
Group By Leaf Expression
button on the main tool bar of the
Dataflow
tool window.

To view the code of assignments and method calls, press the toggle button.
IntelliJ IDEA adds a Preview pane which shows the code of the assignment or call that is currently selected in the tree,
the code is highlighted:

To navigate to the source code of an assignment or call, double click the relevant line in the tree.

Dataflow from Here

The hierarchical view is similar to the results of Dataflow to Here analysis, but the values flow in the opposite direction.